Usage of radio spectrum, or spectrum for short, is regulated independently within different countries, or regions. An authority regulating spectrum usage in a certain region may be referred to as a regulator. Radio communication systems, such as cellular telecommunication systems, are developed and designed for different spectrum ranges, or operating bands. An operating band may be referred to as an operating frequency band.
An operating frequency band supports a specific duplex mode of operation. The possible duplex modes are frequency division duplex (FDD), time division duplex (TDD) and half duplex FDD (HD-FDD). In FDD mode of operation, which is used in Universal Terrestrial Radio Access Networks (UTRAN) FDD and Evolved Universal Terrestrial Radio Access Networks (E-UTRAN) FDD, the uplink and downlink transmission take place on different carrier frequencies. Reference is made to Third Generation Partnership Project (3GPP) TS 25.101, “User Equipment (UE) radio transmission and reception (FDD)”, 3GPP TS 25.104, “Base station (BS) radio transmission and reception (FDD)”, and 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception” and 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Base station (BS) radio transmission and reception”. Therefore, in FDD mode both uplink and downlink transmission can occur simultaneously in time. The carrier frequencies used in the uplink and the downlink are referred to as pass band for uplink and downlink, respectively. The minimum distance in frequency between the uplink and downlink pass bands is referred to as a duplex gap. The distance in frequency between the uplink and downlink carrier frequencies is referred to transmit-receive (TX-RX) frequency separation for the radio transmitter. The TX-RX frequency separation can be fixed, aka default, or variable. In the latter case the TX-RX frequency separation is configurable by the network.
On the other hand in TDD mode, which is used in UTRAN TDD and E-UTRAN TDD, the uplink and downlink transmission take place on the same carrier frequency channel but in different time slots or sub-frames. Reference is made to 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception”, 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Base station (BS) radio transmission and reception” and 3GPP TS 05.05, “Radio Transmission and Reception”.
HD-FDD, which is used in Global System for Mobile Communications (GSM), can be regarded as a hybrid scheme where the uplink and downlink are transmitted on different carrier frequencies and are also transmitted on different time slots. Reference is made to 3GPP TS 05.05, “Radio Transmission and Reception”. This means uplink and downlink transmission do not occur simultaneously in time.
Returning to spectrum usage, one of the objectives of standardizing spectrum usage is to develop an operating band which can, preferably, be used globally. A global operating band leads to several advantages in terms of global roaming, reduced cost of the products due to the economy of scale, simplicity in building products/devices since the same, or at least at limited number of, platforms/devices can be reused globally or regionally etc. For each platform, a lot of research and development is required. Thus, a large number of platforms increase cost. However, certain region specific and even operator specific frequency bands are unavoidable due to the fact that the spectrum availability for mobile services may be fragmented in different countries and even within a country. The mobile services are typically operated by the cellular telecommunication systems. Furthermore, the regulators in each country independently allocate the frequency band in accordance with the available spectrum.
The spectrum below 1 GHz, might be scarce or fragmented due to higher demand by other competing technologies due to its favorable propagation characteristics. The assigned spectrum is eventually standardized in 3GPP in terms of frequency bands so that vendors can develop products, such as base stations and user equipments. Expressed differently, the standardized frequency band is written into 3GPP specifications. Hence, there may be a frequency band that is completely allocated in one region while a different region just allocates part of it. For example, Band 5 is widely used. However, only a sub-band of it is used in Region B, which is called Band 19. Band 5 and band 19 are known from 3GPP terminology. FIG. 1 shows a block diagram illustrating a frequency arrangement for band 5 and band 19. The numbers at the ends of each rectangle indicate frequency in MHz and the arrows in each rectangle indicate uplink for an arrow pointing upwards, and downlink for an arrow pointing downwards. The meaning of the arrows applies to FIG. 2 below as well.
One more example of a scarce or fragmented spectrum portion is that of the frequency allocation in the range of 700 MHz, i.e. 700-799 MHz. In the range of 700 MHz, there is potential for a new frequency band Asia Pacific region (APAC). Related to this new frequency band, it is desired to harmonize the use of a band in the range of 798-806 MHz. This band has previously been used mainly for TV broadcasting. The regulatory work is managed by APT (Asia Pacific Telecommunity) Wireless Group (AWG). Since the agreements made in the AWG are not legally binding for member states of the AWG, each individual country may still implement their own band arrangement.
One arrangement for the band is to use 703-748 MHz in uplink and 758-803 MHz in downlink when using FDD. There is also a TDD allocation for the band covering 698-806 MHz.
APAC is a large region and therefore it is difficult to have the same spectrum allocation in all countries in the region. Thus, in some countries it is expected that the allocation may be a subset of the full band of 798-806 MHz, and in some countries it is expected that the allocation may be the full spectrum of 798-806 MHz. For example, some region (e.g. region B) may allocate only parts of the band for communication according to International Mobile Telecommunications (IMT). As an example, the uplink may be placed in 715-750 MHz and the downlink in 770-805 MHz in region B. FIG. 2 shows another block diagram illustrating the frequency arrangements relating to the 700 MHz band for AWG, say region A, and region B.
An operating frequency band comprises a number of carrier frequencies. The carrier frequencies in a frequency band are enumerated. The enumeration is standardized such that the combination of the frequency band and the carrier frequency can be determined by a unique number called absolute radio frequency number.
In GSM, UTRAN and E-UTRAN the channel numbers are called Absolute Radio Frequency Channel Number (ARFCN), UTRA Absolute Radio Frequency Channel Number (UARFCN) and E-UTRA Absolute Radio Frequency Channel Number (EARFCN) respectively.
In FDD systems separate channel numbers are specified for UL and DL. In TDD there is only one channel number since the same frequency is used in both directions.
The channel numbers (e.g. EARFCN) for each band are unique to distinguish between different bands. The channel number for each band can be derived from the expressions and mapping tables defined in the relevant specifications, such as 3GPP TS 25.101, “User Equipment (UE) radio transmission and reception (FDD)”, 3GPP TS 25.104, “Base station (BS) radio transmission and reception (FDD)”, 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception”, 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Base station (BS) radio transmission and reception”, 3GPP TS 05.05, “Radio Transmission and Reception”. Based on the signaled channel numbers (e.g. EARFCN in E-UTRAN) and the pre-defined parameters associated with each band the UE can determine the actual carrier frequency in MHz and the corresponding frequency band. This is explained by the following example.
For example the relation between the EARFCN and the carrier frequency (FDL) in MHz for the downlink is pre-defined by the following equation in:FDL=FDL_low+0.1(NDL−NOffs-DL)
Reference is made to 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception” and 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Base station (BS) radio transmission and reception”.
Where FDL_low and NOffs-DL are pre-defined values for each band and NDL is the downlink EARFCN.
Consider E-UTRA band 5, whose EARFNC range (NDL) as pre-defined in the specifications above lies between 2400-2649. The pre-defined values of FDL_low and NOffs-DL are 869 and 2400 respectively. Assume the network signals downlink EARFCN to be 2500. Using the above expression the UE can determine that the downlink carrier frequency of the channel is 879 MHz. Furthermore, as stated above that the pre-defined EARFNC range being unique for each band, hence the UE can determine the frequency band corresponding to the signaled EARFNC. An expression to derive the E-UTRA FDD uplink carrier frequency, which is similar to that of the downlink carrier frequency, is also pre-defined. In E-UTRA FDD both fixed transmit-receive frequency separation (i.e. fixed duplex) and variable transmit-receive frequency separation (i.e. variable duplex) are supported. If fixed transmit-receive frequency separation is used by the network then the network does not have to signal the uplink EARFCN since the UE can determine the UL carrier frequency from the downlink carrier frequency and the pre-defined duplex gap. In an event the variable duplex is employed by the network for a certain band then both DL and UL EARFCN have to be signaled.
In the following, the use of channel number indication for mobility is explained.
In order to simplify the frequency search, or the so-called initial cell search, a center frequency of a radio channel is specified to be an integral multiple of a well defined, generally fixed, number, called channel raster. This enables UE to tune its local oscillator only at one of the raster points assuming it to be the center frequency of the channel being searched.
The channel raster in UTRAN FDD is 200 KHz but for certain channels and bands it is also 100 KHz. In E-UTRAN FDD and TDD, the channel raster for all channels and bands is 100 KHz. The channel raster directly impacts the channel numbering, which is described in the next section.
For the initial cell search or more specifically for the initial carrier frequency search the UE has to search at all possible raster frequencies e.g. with 100 KHz resolution in E-UTRAN frequency band. However for the UEs camped on or connected to the cell, the network signals the absolute radio frequency channel number(s) for performing measurements, mobility decisions such as cell reselection or commanding handover to certain cell belonging to certain frequency channel of the same or of different Radio Access Technology (RAT) etc.
Hence, the UE after camping on a cell in idle mode or when connected to a cell in connected mode can acquire the cell specific or UE specific system information, which contains information such as frequency band number (frequency band indicator), absolute radio frequency channel number(s) etc. More specifically in LTE the band number and the ARFCN (e.g. UL EARFNC in LTE) is signaled to the UE over the relevant system information blocks (SIB). For example in LTE the band number and the EARFCN of the cell are signaled to the UE over SIB1 and SIB2 respectively.
The SIB1 uses a fixed schedule with a periodicity of 80 ms and repetitions made within 80 ms. The first transmission of SIB1 is scheduled in sub-frame #5 of radio frames for which the SFN mod 8=0, and repetitions are scheduled in sub-frame #5 of all other radio frames for which SFN mod 2=0. The SIB1 also contains the scheduling information of the remaining SIBs e.g. SIB2, SIB3 etc. This means SIB2 scheduling information is determined by the UE by acquiring SIB1, which is transmitted with a periodicity of 80 ms. The contents of the SIB1 and SIB2 in LTE are known in the art.
The network can request the UE to perform handover to another frequency or another RAT in the frequency band, which can either be the same or different than the carrier frequency of the serving cell. Therefore, in order to assist the UE to perform the inter-frequency or inter-RAT handover the network signals the frequency channel number of the target carrier frequency in the handover command. For example for the UE in the connected mode the network the eNode B in LTE signals the SIB2 to the UE using the UE specific channel.
The standardization of a frequency band encompasses various aspects including the band numbering, raster, carrier frequency channel numbering, radio requirements for user equipments and base stations, performance requirements for user equipments and base stations, radio resource management (RRM) requirements etc. Some or all of these factors have to be taken into account by a manufacturer of for example user equipments and radio base stations. Examples of radio requirement for user equipments are requirement concerning out of band (OOB) emission, radio frequency (RF) exposure to human and more. As an example, performance requirements for user equipments and base stations may relate to mobility, e.g. mobility procedures, handover, cell reselection or the like.
The design and implementation of a duplexer becomes more difficult depending upon various factors. Notably, if a pass band is wide and if a duplex gap of the band is small, attenuation requirements in stop-band becomes large. The attenuation requirements relates to requirements for OOB, RF exposure and the like. The stop-band defines a frequency range in which reduced, or at least less than some threshold value, transmission from the transmitter is desired. As an example, an attenuation requirement may be a threshold level for OOB. In case of FDD 700 MHz, with full spectrum allocation, the pass band is very wide, i.e. 45 MHz in each direction, and the duplex gap is small. Presently, it is suggested that a user equipment configured for operation in such operating frequency band will use two duplexers. As a result, the attenuation requirements are believed to be fulfilled.
As mentioned above, a frequency band in the range of for example 700 MHz may have full spectrum allocation in certain regions, which herein are referred to as region A. On the other hand in some other regions, the spectrum allocation may be subset of the full band. Such regions are referred to as region B herein. Therefore, an issue is how to handle spectrum allocation in different regions.
To address this issue a first known solution is to define one frequency band based on the largest allocation. This approach simplifies mobility, such as roaming, and ensures the economy of scale, i.e. there is no need for devices designed, or configured, for specific regions. However, due to large allocation in full band, e.g. FDD UL/DL: 2×45 MHz with 10 MHz duplex gap, the user equipment will require two duplex filters to cover the entire band as mentioned above. This will increase the cost for user equipments in regions where it would be sufficient to have single duplexer in the user equipment due to partial allocation of the band. That is, cost of user equipments operating in region B will be unnecessarily high.
Therefore, in order to reduce cost of the user equipment operating mainly in region B, two bands are defined according to a second known solution. A first band band_X covers the entire frequency range, or the full spectrum, and a second band band_Y covers a subset of the full spectrum. Advantageously, cost of user equipments configured for region B may be kept lower since only one duplexer is needed. FIG. 3 shows a further block diagram illustrating another exemplifying frequency arrangement for the first band band_X, applied in region A, and the second band band_Y, applied in region B. In this general example, the first band band_X is an allocation to the full spectrum, or full band, and the second band band_Y is a partial allocation of the full spectrum. In this manner, multiple bands for overlapping frequency regions, or ranges, are defined.
A disadvantage of the second known solution is that a user equipment, supporting only a portion of the band, is not able to operate in a region where the entire band is allocated. Expressed differently, roaming of devices, such as the user equipment, between different regions is hampered.